We have been studying the mechanism of myocardial depression caused by general anesthetics. Through our past studies, we were able to identify at least three sites of action of these drugs, i.e.: plasma membrane, sarcoplasmic reticulum (SR) and contractile proteins. Since the SR directly controls the CA++ flux in muscle, and since anesthetic effects in this system are largely unknown, we propose to study the effect of general anesthetics on the SR. Our new hypotheses are that general anesthetics at clinically used concentrations do not interfere with the CA++-uptake of the SR, but they enhance CA++-triggered CA++-release from the SR. The enhancement of the CA++-release lowers the CA++ content of the SR, thereby causing their well-known negative inotropic effect. We will test these hypotheses by combining the biochemical study of CA++-triggered CA++-release and the biophysical measurements of the membrane phospholipid fluidity (using spin-probe EPR spectroscopy) and of the rotational mobility of the CA++-ATPase protein (with saturation transfer EPR spectroscopy).